Microporous nonadherent surgical dressing

ABSTRACT

A composite surgical dressing that is highly absorbent, capable of preventing leakage or exudation from open wounds and capable of preventing contamination from entering or escaping from the wound, comprising an outer microporous, liquid-repellent fibrous layer having a maximum pore size of 0.5 micron, and a voids volume of at least 50 percent; an inner macroporous, fibrous layer, the body-contacting face of which is non-wetted by body fluids; and a highly absorbent intermediate layer between the outer and inner layers.

United States Patent 1191 Riely Jan. 9,1973

MICROPOROUS NONADHERENT SURGICAL DRESSING Inventor: Phyllis Riely,Massapequa, N.Y. Assignee: Pall Corporation, Glen Cove, N.Y.

Filed: Nov. 21, 1969 Appl. No.2 878,716

U.S. c1 Q. ..128/156 1m. (:1. ..A6ll 15/00 Field of Search ..l28/l56,155, 296

References Cited UNITED STATES PATENTS Gallovich 128/156 Bierenbaum etal. ..l28/l56 Gander et a1 ..l28/l56 X OTHER PUBLICATIONS PioneeringUses of Fiberglas Materials in Medicine, Owens-Corning Fiberglas Corp.(3/21/45).

Meier ..l28/l56 Primary Examiner-Robert W. Michell Attorney-lanes andChapman [5 7] ABSTRACT A composite surgical dressing that is highlyabsorbent,

capable of preventing leakage or exudation from open wounds and capableof preventing contamination from entering or escaping from the wound,comprising an outer microporous, liquid-repellent fibrous layer having amaximum pore size of 0.5 micron, and a voids volume of at least 50percent;- an inner macroporous, fibrous layer, the body-contacting faceof which is non-wetted by body fluids; and a highly absorbentintermediate layer between the outer and inner layers.

11 Claims, 2 Drawing Figures MICROPOROUS NONADHERENT SURGECAL DRESSINGDressings are applied to large area wounds, whether massive abrasions orburns or deep open wounds, in order to protect the wound surface, absorbfluids exuded from the wound and to let air into the surface of thewound. It is important to prevent the contamination of the wound withoutimpeding the progress of the natural healing process of the body, and insome cases, to protect the environment against contamination from thewound.

It is also important to avoid, or at least impede, the formation of anadherent bond between the wound surface and the bandage; such a bond canbe formed when the body fluids exuded from the wound into the dressingdry to a crust and the dry crust adheres to the healing flesh and to thedressing. This makes very difficult the removal of the bandage withoutcausing great pain to the patient and, even more important, withoutreopening a partially healed wound.

A further problem is absorbing the body fluids which tend to exude froman open wound or massive burn area, so as to remove the fluids from thesurface of the wound, permitting it to dry; this furthers the healingprocess; it is also necessary at the same time to control the loss offluid. It is most advantageous, especially when dealing with massiveburns, to insure against shock by preventing the excessive loss of thesalts from the body which generally are dissolved an any body fluidswhich may be exuded. Therefore, by limiting the loss of body fluids, theloss of salts is also impeded, thereby decreasing the chances of severeshock.

Previous attempts have been made to prepare bandages which areimpermeable to the passage of liquids, but selectively permeable tospecific gases and vapors. In US. Pat. No. 3,367,329, patented Feb. 6,1968, to Dibelius, there is described a surgical bandage including anonporous membrane, impermeable to liquids and infectious organisms butselectively permeable to specific gases and vapors. In other words, thematerial is a membranous material that permits the diffusion of vapors,which diffusion is due to the partial pressure differential and is notrelated to the conventional filtering process (column 2, lines 67 and68). Such a material is insufficiently permeable compared to the usualporous bandage material, and thus fails to provide the necessarytranspiration from the wound surface. Further, there is no provision forabsorption of any body fluids exuded from a wound or burn area. TheDibelius membrane is indicated as being a thin, permeable siliconerubber membrane having the desired permeability. I

U.S. Pat. No. 3,426,754, patented Feb. H, 1969, to Bierenbaum et a].describes a medicaldressing comprising a film having apressure-sensitive adhesive applied thereto. The film is described as aporous material having an open celled structure permeable to gases. Thevoid or pore sizes of the open cell structure accessible to the exteriorof the film is described as being under 5,000 angstrom units, e.g., 100to 500 angstrom units. The film of Bierenbaum et al. is prepared from agroup of relatively crystalline film-forming polymers having a definedelasticity. These films are prepared by a special process which formsthe open cell structure in the film. The film can be formed from varioushydrocarbon polymers, acetal polymers or a miscellaneous group ofpolymers including polyalkylene sulfides, polyphenylene oxides,polyamides polyesters. Films of this type are also relativelyinefficient and fail to provide the necessary amounts of air andmoisture vapor to and from the wound surface; they have a low dirtcapacity, so that the amount of air which can be passed in quicklydecreases once the film is exposed to even a slightly dusty environment.Bierenbaum et a1. further disclose the use of the porous film incombination with a pad or facing, covered by a wrapping or cover whichfunctions to hold the facing in position.

It is an object of the present invention to provide a surgical dressingwhich provides all of the usual at-' tributes of a surgical dressing,including the ability to absorb the body fluids exuded from the wound,to protect the wound surface, and to permit the transpiration of air andmoisture between the atmosphere and the wound surface. It is a furtherobject of the present invention to provide a surgical dressing which, inaddition to all of the usual attributes of a surgical dressing, alsoprevents the passage of microorganisms to or from the wound surfacewhile retaining the ability to permit full transpiration of air andmoisture during use.

it is a further object to provide a surgical dressing which is highlyabsorbent and capable of retaining, after absorbing, the body fluidsexuded from the wound, so as to prevent the passage of the exuded liquidoutside of the bandage.

In accordance with the present invention, a composite surgical dressingis provided comprising an outer microporous, liquid repellent fibrouslayer, an intermediate absorbent layer, and an inner macroporous layerfor separating the absorbent layer from a wound. The body-contactingface of the inner layer is 1 not wetted by body fluid and thus has theproperty of being relatively non-adherent to a wound surface.

The dressing according to this invention is especially useful for largeopen wounds or massive burn areas,

where there is heavy exudation of body fluids from the wound which mustbe absorbed, and the loss of which must be controlled and limited,together with a need for maintaining the wound or burn area aseptic andfree from dirt, dust or other contaminants or irritants. It is furtheruseful to prevent the influx of liquids from the exterior whilepermitting the free passage of air to the wound surface. The surgicaldressing has a large capacity to absorb exuded body liquids withoutpermitting loss of such liquids through the upper layer of the dressing,thus controlling the loss of fluids and the salts dissolved therein fromthe body.

The three layers of the composite'surgical dressing of this inventioncan be held together by mechanical means or by a bonding agent.Optimally, the layers are bonded together around their periphery, or atthe outer edges of the composite. This avoids obstructing or decreasingthe absorbency of the central layer of the dressing at the centralportion which will be over the wound area. Holding or bonding the layerstogether around their periphery so that the edges of the dressing aresealed also serves to prevent any loss or escape of the centralabsorbent layer from between the inner and outer layers; this isespecially important where the absorbent layer is formed of a fluffyfibrous mass in which and the individual fibers are not bonded together.Further, imperviously sealing the edges prevents the entry of bacteriaor other contaminants into the absorbent layer; this prevents thecircumvention of the protective upper, microporous, liquid-repellentlayer by these contaminants.

The surgical dressing preferably also comprises an adherent layer, whichserves to bond the dressing pad to the flesh of the user; the adherentlayer preferably bonds the dressing pad to the flesh of the patient,around the periphery of the wound, to complete the seal around theperiphery of the dressing; this further inhibits the by-passing of themicroporous outer layer by organisms or particles that could contaminatethe wound surface.

The outer microporous fibrous sheet of the dressing of the presentinvention must be liquid-repellent, to

' water. Thus, if the outer layer were not liquid repellent,

as moisture condenses or is deposited upon the exterior of the outerlayer, bacteria could be carried by the water through the pores oftheouter fabric into the absorbent layer and then to the open wound or burnsurface. It is a well-known fact that filters can retain airborneparticles of a smaller size than liquid-borne particles. A largeliquid-borne particle can be pushed through the filter pores by theflowing liquid that could not be pushed through by dry air. Accordingly,the pores need be no smaller than the largest dimension of amicroorganism or particle.

The microporous fibrous outer layer of the dressing of the presentinvention provides an open passage for the atmosphere to the spacewithin the dressing, and especially that immediately above the wound.-The outer microporous layer is sufficiently porous to permit the passageof air at a substantially zero pressure differential across the surface.The outer layer does not pass the air by a diffusion process, as in thecase of a membrane, but rather by direct gas flow through open pores.The outer layer must have a fluid flow capacity sufficient to maintaintranspiration over the-wound area. The open structure of the microporousfibrous layer is obtained by utilizing a filter material having a voidsvolume of at least 50 percent and preferably at least 75 percent.

The outer fibrous layer preferably has a pore size which excludes thepassage of air-borne particles of greater than 0.5 micron diameter andoptimally of greater than 0.2 micron diameter. This is referred to inthe claims as effective maximum pore diameter. This is sufficientlysmall to prevent the passage of substantially all harmful air-bornebacteria or other microorganisms such as molds, fungi and spores. Theliquidrepellent properties of the outer fibrous layer prevent thepassage of liquid and thus a smaller pore size is unnecessary.

The outer microporous fibrous layer of the present invention must alsobe capable of withstanding the abrasion to which it may be subjectedduring useQFor example, if worn by an ambulatory patient, who thenproceeds to carry out his normal daily activities wearing the surgicaldressing, the outer layer can be subjected to severe abrasive stress.The outer layer must have sufficient wear resistance to maintain itsuseful ness over a period of time when worn by an active pattent.

Accordingly, preferred types of microporous liquidrepellent fibrouslayers are prepared from a woven glass cloth, which gives the fabricgreat abrasion resistance and flexibility; the glass cloth preferablyhas deposited within the weave glass fibers which are bonded in placewith a fluorocarbon polymer, including a chlorofluoroc arbon polymer,impregnant or a silicone impregnant. The impregnants are preferablyinert and nontoxic to the patient. These impregnants areliquid-repellent and thus prevent the passage of aqueous liquids throughthe microporous fabric. The glass fabric has great strength and abilityto withstand the stresses to which it would be subjected during a dayswearing by an ambulatory patient. An example of such a material isdescribed in U.S. Pat. No. 3,053,762, patented Sept. 1 l, 1962 toAdiletta.

Examples of suitable fluorocarbon and chlorofluorocarbon polymerimpregnants include polytetrafluoroethylene, fluorinatedethylenepropylene polymer, polyhexafluoropropylene andpolychlorotrifluoroethylene. Polytetrafluoroethylene is the preferredimpregnant.

The silicone impregnants can be silicone resins or silicone rubbers. Thedimethylsiloxane polymers are preferred because of their physiologicalinertness.

The use of a woven glass fiber fabric and deposited glass fibers isespecially preferred, when utilizing a fluorocarbon polymer impregnant.The fluorocarbon polymers require a relatively high curing temperature,

after impregnating the fabric to cure the polymer and to bond the fibersin place; glass is especially suited to withstand such hightemperatures. Other impregnating fibers and woven fiber fabrics,however, can be used including such synthetic fibers, and fabrics madetherefrom, such as polyamides, polyesters, rayons and polyacrylic resinsand even such natural fibers as wool and cotton. The siliconeimpregnants are especially useful when the fabric and the impregnatingfibers are not formed of glass because the silicone impregnants do notrequire a high curing temperature.

Nonwoven fabrics can also be utilized for the upper layer of thedressing of this invention if they are strong enough and have sufficientabrasion resistance. Excellent microporous woven and nonwoven fibroussheet materials can be prepared according to any of the following U.S.Pat. Nos. 3,238,056 to Pall et al., dated Mar. 1, 1966; No. 3,246,767 toPall et al., dated Apr.

bency required. Preferred materials include folded crepe tissue ofcotton fibers or of wood pulp fibers, cotton wadding, certain syntheticfibers such as acetate rayon or regenerated cellulose, pulp fluff fibers(obtained by disintegrating chemical cellulose pulp prepared by thesulfate or sulfite methods in such a way that the fibers are set freefrom the pulp while at the same time avoiding the formation of fiberbundles or knots and cutting of the fibers), absorbent cotton fluff,such as cotton linters, garnetted white cotton waste, and fibrous layersformed from ramie, jute, hemp and bagasse fibers.

The absorbent portion can be formed of mats or pads of fibers, such as amixture of cotton linters and crimped viscose rayon staple fibers, eg inthe proportions of about 60 percent cotton linters and 40 percentviscose rayon staple fibers by weight. The fibers can have a denierwithin the range of from about 3 to about 15.

Cotton linters comprise cotton fibers of short length usually within therange of one thirty-second to about three-sixteenths of an inch. Theviscose rayon fibers are preferably crimped or crinkled and generally oflonger lengths, for example from about one-fourth to about three-fourthsinch. The viscose fibers tend to add additional resiliency, if needed,to the absorbent layer to further protect the wound area. In addition,if the absorbent material is to be compressed, which results in agreater absorptivity per volume of absorbent material, the rayon fibercomponent permits additional resilience or springiness in the absorbentpad.

Generally, any highly absorbent, usually cellulosic fibrous material ofabulky character can be used as the absorbent layer in the dressing ofthe present invention. Although noncellulosic materials can be used,they are not as preferred because the fibers, per se, are. generallynonabsorbent, or if they are absorbent tend to be far more expensivethan the cellulosic materials.

Certain sponge materials, such as an artificial regenerated cellulosicsponge as conventionally produced and commercially available, havesuitable properties of texture, porosity, resilience and absorptivitysuitable for use as'an absorbent layer in the dressing of the presentinvention. Composite fiber-surfaced sponges, such as are described inUS. Pat. No. 3,156,242, patented Sept. 3, 1968, to Crowe, Jr. et al.,having hydrophilic fibers extending from the surface of the sponge intothe main body thereof, are especially useful for forming the absorbentlayer of the dressing of the present invention. Generally, anyhydrophilic material is useful for the absorbent layer, including anycombination of the above fibrous and/or spongy materials.

The inner layer of the dressing of the present invention, which isintended to contact the wound area, is of a macroporous fibrous sheetmaterial, preferably woven to obtain increased strength and greatestporosity, and nonadherent to the wound. The porosity must be greatenough to allow body fiuids to pass through the pores with insufficientpressure drop, despite the non-wetted characteristic, and small enoughto prevent fibers of the absorbent layer from extending through tocontact the wound. It is important that the inner face of the innerlayer, which is intended to rest against the wound area, be nonadherentto the wound surface.

Otherwise, fibers might be left behind on the wound, causing possiblefuture complications, and the dressing might tend to pull open apartially healed wound, when being pulled off. To avoid this problem,the fibers on the body-contacting face of the inner layer, i.e. the faceintended to rest against the wound, are formed of, or coated orimpregnated with, a material which is not wetted by body fluids, so thatwhen the body fluids dry, they do not form an adherent bond to that faceof the layer.

The macroporous, non-wetted, physiologically inert inner layer ispreferably formed of a loosely woven glass fiber scrim. Other fibrousmaterial can be used, including the various fabrics listed above for themicroporous outer layer. The inner fabric is preferably impregnated, atleast on the body-contacting face, with a nonadherent, physiologicallyinert, liquid-repellent polymer such as the fluorocarbon, including thechlorofiuorocarbon, polymers or silicone polymers discussed above as theimpregnant for the microporous outer layer. All of the body-contactingface of the inner layer must be non-wetted by body fluids, to insurethat it is nonadherent, and macroporous. Hence, any impregnation shouldcover the fibers forming the outer' face of the fabric, i.e. the facetouching the wound area, but should not block the pores between thefibers. Generally, polytetrafluoroethylene is the preferred impregnatingagent. for the nonadherent lower layer, because of its inertness, andits ability to form a thin film on the fibers of the fabric, withoutblocking the pores.

Alternatively, the fibers forming the coarse fabric can be coated withthe liquid-repellent preliminary to formation of the fabric, whether byweaving, knitting or laying down to form a nonwoven web or mat, toinsure that all of the fibers are completely coated. This, however, mayrender more difficult the fabric forming process, as the coated fibersmay not be as easily handled because they become too thick.

The use of a polytetrafluoroethylene impregnation on the innermacroporous layer, as with the upper layer, tends to favor theutilization of a glass fabric, or other inorganic hightemperature-resistant material. A preferred material for forming thelower layer is a coarsely woven glass fiber fabric which is coated withTeflon and then cured at the high temperatures required for Tefloncuring.

Making the inner fabric layer non-wetted by body liquid and non-adherentto the open wound enables the bandage to be removed without reopening alarge oozing wound. The liquid being exuded from the wound surface flowsthrough the macroporous inner layer, to

be absorbed by the intermediate layer. The inner layer is not wetted bythe liquid exuded from a wound, and

separates the absorbed liquid in the absorbent layer from the woundsurface. The liquid absorbed by the absorbent layer is thus separatedfrom the wound area by the non-wetted inner fabric layer, so that whenthe abupper and lower fabric surfaces. Preferably, the tape ismicroporous, as is the upper fabric, or non-porous to air so as toprevent the passage of microorganisms.

Alternatively, the upper and lower layers can be bonded together byapplying a bonding agent to the layers and pressing them together, andcuring the bonding agent, if necessary. Preferably, the microporouslayer extends out beyond the absorbent layer and is folded around andunder the inner macroporous layer. This latter system is desirable,because it protects the absorbent layer from being contaminated and thusprevents contaminants from being absorbed by the absorbent layer andpassing through the macroporous layer to the wound surface.

The dressing pad can be attached onto a patient in various ways. Anadhesive layer can be applied to the dressing pad. The adhesive can beapplied around the outer periphery of the lower fabric layer; it can beapplied to the lower side of the tape that is folded around the edges ofthe dressing pad, if that is the method used to hold the compositetogether; or, it can be applied to a portion of the upper microporouslayer if the upper layer extends out beyond the main body of the pad orif the upper microporous layer is folded around and under the lowermacroporous layer. Alternatively, the composite dressing can be appliedto a patient and held in place by a bandage, generally a coarsely wovenfabric, or by tape, wrapped about the patient.

Referring to the drawings,

FIG. 1 is a perspective view of a dressing pad prepared according to thepresent invention with portions of the upper microporous layer and ofthe middle absorbent layer broken away.

FIG. 2 is a sectional side view of the dressing pad of F IG. 1.

In the drawings, the upper microporous fabric 1 is a woven glass clothhaving glass fibers deposited in the weave and impregnated with Teflon.The fabric is prepared according to the procedure set out in the Examplein U.S. Pat. No. 3,053,762, utilizing a polytetrafluoroethyleneimpregnant. The microporous layer 1 has a maximum effective pore size of0.2 microns, as determined by 100 percent removal of the bacteriaPseudomonas Diminutia in air suspension.

The middle absorbent layer 4 is formed of compressed wood cellulosefluff deposited as a layer upon the upper microporous fabric and held inplace between the lower macroporous woven glass scrim 3 and the upperfabric. The scrim 3 is formed ofa woven glass fabric impregnated withpolytetrafluoroethylene to insure body liquid repellency. in forming thedressing, the glass scrim is placed over the layer of fluff depositedupon the microporous layer 1 and the composite is compressed to decreasevolume and thus increase unit-volume absorptivity. Finally, themicroporous adhesive tape 2 is attached around the periphery of thedressing and folded over to bind the structure together and to maintainthe middle fluff layer in compression. Folding the tape 2 completelyaround the periphery of the pad insures against loss of the middle flufflayer 4. However, folding the tape around only two of the four sidescould be sufficient.

Alternatively, the middle layer can be formed of folded sheets of cottonwadding or wood pulp crepe tissue or several layers of a nonwovenfibrous material interleaved between supporting sheets of woven fabricssuch as gauze; this type of an absorbent layer can be precompressed andthen held between the microporous and macroporous outer layers; thecomposite can be then held together as explained above.

Alternatively, as a substitute for the microporous tape 2, which isapplied around the sides and folded over both the upper and lower layeras shown in the drawing, the upper and lower macroporous and microporousfabrics can be bonded together with a bonding agent applied around theedges of the fabrics and cured subsequent to placing the absorbent layerbetween the two outer layers.

To further prevent contamination of the wound area and to prevent escapeof wound exudation, means should be provided for sealing the peripheryof the inner layer of the dressing to the flesh of the patient.

Such sealing means can include an adherent area around the periphery ofthe dressing, such as is shown in the drawing in FIG. 1, where the tape2 folded around the inner and outer layers can have a portion of itsundersurface, 5, i.e. adjacent. the outer face of the inner layer 3,adhesive on two sides, such that when it is pressed against the patientthe outer edges will adhere to the patient forming an air-tight, orpreferably a microporous, water-resistant bond. Preferably the adhesivematerial is permeable or porous to air but non permeable tomicroorganisms. The permeable or porous adhesive is formed so as toautogenously develop a vast number of pores producing a microporous,adhesive film that remains visibly continuous, but provides amicroporous adhesive web suitable to prevent the contamination of thearea under the dressing when the dressing is applied and bonded to apatient. Such a microporous adhesive is capableof admitting air, even tothe area directly under the adhesive, thereby preventing any macerationof the wound border area, but prevents the passage of bacteria. Suchmaceration of the skin often occurs when a nonporous layer is appliedover the skin, preventing the skin from transpiring properly. Suchmaceration is evidenced by a wrinkling and paleness of the flesh. Anespecially useful embodiment of such adhesive is shown in U.S. Pat. No.3,426,754, to Bierenbaum et al., see particularly, the portion beginningon column 7, line 57 through column 8, line 60.

As a further preferred embodiment of the invention, a germicide can beapplied either to the absorbent layer or to'the outer microporous layerof the dressing. Such a germicide would insure that any microbes whichdo penetrate the outer layer will be inactivated or killed. Thegermicide should, of course, be nontoxic and nonirritating to thepatient. However, if the germicide is applied to the outer microporouslayer or the the upper portion of the absorbent layer immediatelyadjacent the outer layer, and it cannot migrate through the absorbentlayer and macroporous inner layer, to contact the patient, thenonirritating nature. of the germicide becomes less significant.

Antiseptic or medicating agents or other biologically active agents canbe introduced into the dressing, especially into the macroporous layeror the absorbent layer, by incorporating a liquid or dry medicatingagent and applying it to the desired layer. Such materials can be coatedon the inner layer so as to react with the fluids exuded from the woundand thus be applied to aid in healing and disinfecting the woundsurface. The germicide is preferably applied to the outer layersubsequent to curing, especially if the impregnant in the outermicroporous layer is a tetrafluoroethylene polymer. Such materialsrequire a high curing temperature which would decompose most organicgermicides. Further, a disinfectant or biocide which is intended to acton the wound surface by reacting with the body fluids to eitherdisinfect the wound area or to aid in the healing process can be appliedto the inner macroporous layer, also subsequent to application andcuring of the liquid-repellent coating to impart the nonwettedcharacteristic.

The fibrous layers and the composite dressing should be flexible, so asto be able to conform to the bodys surface. Where desirable, such aswhere the dressing is to be placed over an area which is subject toconstant flexing, as at a joint in the body, e.g. an elbow or a knee, sothat the dressing would require an added degree of flexibility, thefibrous layers can be formed only in part of the microporous ormacroporous fabric, having intermediate portions formed of animpermeable, but elastic, material. In this construction, themicroporous or macroporous fabric material can be formed in alternatingstrips along the length of the dressing, extending in a directionperpendicular to the direction in which the dressing is to be flexed,with the portions intermediate the microporous or macroporous materialformed of the elastic material. This increases the elasticity of thedressing subjected to extreme flexing by the bodily member, whilelimiting the stress on the microporous or macroporous material, therebydecreasing the chances of ripping the microporous or macroporous layers,or of expanding or warping the pore openings of the layers, and therebyexposing the wound to exterior contaminants.

The intermediate absorbent layer, if it is highly porous to the flow ofair, can aid to ensure that the air passing through the permeableportions of the outer layer is distributed over the entire surface ofthe wound, through the microporous outer layer and the macroporous innerlayer. Generally, however, to permit the greatest amount of air to passover the wound area, it is preferred that all of the outer layer beformed of the microporous material, which must, therefore, besufficiently supple to withstand almost continuous flexure.

The inner macroporous layer should also be elastic, in this situation.However, because there is no need to avoid stretching the pores of thematerial or to avoid warping it in any way, the fabric itself may bemade elastic, or it can be formed, at least in part of elastic fibers.Methods of preparing both woven and nonwoven elastic materials are wellknown to the art.

Having regard to the foregoing disclosure, the following is claimed asthe inventive and patentable embodiments thereof:

1. A composite surgical dressing having a high degree of absorbency forbody fluids exuded from a wound area, capable of preventingmicrobiological contamination of the wound area from without, andnonadherent to the wound during healing, comprising an outer microporousliquid-repellent fibrous layer having an effective maximum pore size notin excess of ill 0.5 micron, inhibiting passage of body fluids andpassage of microorganisms in either 1 Y direction therethrough, andhaving a voids volume of at least 50 percent, an inner macroporousfibrous layer, the bodycontacting face of which is permeable to but notwetted by body fluids and impregnated so as to coat the fibers thereofwith a nonadherent physiologically inert liquid- 1 repellent polymerthereby rendering the body-contacting face nonadherent to the wound, andbonding the fibers of the face together, and a highly absorbentintermediate layer between the outer and inner layers capable ofabsorbing body fluids passing through the inner macroporous layer.

2. The dressing of claim 1 wherein the outer and the inner layers arebonded together so as to compress the absorbent layer between them.

3. The dressing of claim 2 wherein the outer and inner layers are bondedtogether by an adhesive tape applied around the edges of the dressingand folded over each of the outer and inner layers.

4. The dressing of claim 1, including an adhesive applied to the outsidesurface of the inner layer of the dressing, around the peripherythereof, to bond the dressing to a patient.

5. The dressing of claim 1 comprising in addition a biologically-activeingredient applied to one of the layers of the dressing.

6. A composite surgical dressing having a high degree of absorbency forbody fluids exuded from a wound area, capable of preventingmicrobiological contamination of the wound area from without, andnonadherent to the wound during healing, comprising an outer microporousliquid-repellent glass fiber fabric fibrous layer having an effectivemaximum pore size not in excess of 0.5 micron, inhibiting passage ofbody fluids and passage of microorganisms in either directiontherethrough, and having a voids volume of at least 50 percent, an innermacroporous fibrous layer, the body-contacting face of which is notwetted by body fluids and impregnated so as to coat the fibers thereofwith a nonadherent physiologically inert liquidrep'ellent polymerthereby rendering the body-contacting face nonadherent to the wound, andbonding the fibers of the face together, and a highly absorbentintermediate layer between the outer and inner layers capable ofabsorbing body fluids passing through the inner macroporous layer.

7. The dressing of claim 6 wherein the glass fiber fabric has glassfibers embedded in the weave thereof.

8. The dressing of claim 6 wherein the glass fiber fabric is coated witha resinous material imparting liquid repellency to the fabric. i

9. The dressing of claim 6 wherein the inner fibrous layer is a coarselywoven glass fiber fabric coated with a fluorocarbon resin impartingliquid repellency to the fabric and improving its resistance to adhesionto the body, while permitting the passage of fluids and air through thefabric.

10. The dressing of claim 6 wherein the outer layer is microporous glassfiber fabric impregnated with glass fibers and a fluorocarbon resinimparting liquid repel lency to the fabric, the'intermediate layer is alayer of absorbent cellulose fibers, and the inner layer is amacroporous glass fiber fabric having the body-contacting faceimpregnated with a fluorocarbon resin imparting liquid repellency to thefabric and improving its resistance to adhesion to the body, whilepermitting the passage of fluids and air through the fabric.

1 1. The dressing of claim 1 wherein the microporous layer has aneffective maximum pore diameter of less than 0.2 micron.

2. The dressing of claim 1 wherein the outer and the inner layers arebonded together so as to compress the absorbent layer between them. 3.The dressing of claim 2 wherein the outer and inner layers are bondedtogether by an adhesive tape applied around the edges of the dressingand folded over each of the outer and inner layers.
 4. The dressing ofclaim 1, including an adhesive applied to the outside surface of theinner layer of the dressing, around the periphery thereof, to bond thedressing to a patient.
 5. The dressing of claim 1 comprising in additiona biologically-active ingredient applied to one of the layers of thedressing.
 6. A composite surgical dressing having a high degree ofabsorbency for body fluids exuded from a wound area, capable ofpreventing microbiological contamination of the wound area from without,and nonadherent to the wound during healing, comprising an outermicroporous liquid-repellent glass fiber fabric fibrous layer having aneffective maximum pore size not in excess of 0.5 micron, inhibitingpassage of body fluids and passage of microorganisms in either directiontherethrough, and having a voids volume of at least 50 percent, an innermacroporous fibrous layer, the body-contacting face of which is notwetted by body fluids and impregnated so as to coat the fibers thereofwith a nonadherent physiologically inert liquid-repellent polymerthereby rendering the body-contacting face nonadherent to the wound, andbonding the fibers of the face together, and a highly absorbentintermediate layer between the outer and inner layers capable ofabsorbing body fluids passing through the inner macroporous layer. 7.The dressing of claim 6 wherein the glass fiber fabric has glass fibersembedded in the weave thereof.
 8. The dressing of claim 6 wherein theglass fiber fabric is coated with a resinous material imparting liquidrepellency to the fabric.
 9. The dressing of claim 6 wherein the innerfibrous layer is a coarsely woven glass fiber fabric coated with afluorocarbon resin imparting liquid repellency to the fabric andimproving its resistance to adhesion to the body, while permitting thepassage of fluids and air through the fabric.
 10. The dressing of claim6 wherein the outer layer is microporous glass fiber fabric impregnatedwith glass fibers and a fluorocarbon resin imparting liquid repellencyto the fabric, the intermediate layer is a layer of absorbent cellulosefibers, and the inner layer is a macroporous glass fiber fabric havingthe body-contacting face impregnated with a fluorocarbon resin impartingliquid repellency to the fabric and improving its resistance to adhesionto the body, while permitting the passage of fluids and air through thefabric.
 11. The dressing of claim 1 wherein the microporous layer has aneffective maximum pore diameter of less than 0.2 micron.